Hydraulic pressure control circuit for a working machine

ABSTRACT

When a working implement comes close to a cab during operation, for efficiency, the operation should continue insofar as possible yet it is essential the working implement be prevented from striking the cab. To that end, a pilot pump oil line capable of supplying pilot pressurized oil to a solenoid proportional pressure reducing valve in a state where a control member is not manipulated, is provided in a stick contraction-side pilot oil line. When the working implement enters an interference prevention area, defined around the cab, the stick is automatically moved out so that the operation can continue yet the working element avoids the interference prevention area.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a technical field of a hydraulic controlcircuit for working machines, such as hydraulic shovels.

2. Description of Related Art

In some working machines, such as hydraulic shovels, an offset-typeworking implement capable of swinging to the left and right is attachedto a machine body. Generally, such working machines accompany a riskthat when the working implement is moved, it may contact, or interfere,with an operator's seat portion. In such working machines, therefore,consideration must be paid to avoiding contact between the workingimplement and the operator's seat portion.

To that end, there has hitherto been proposed a working machine havingattitude detecting means for detecting an attitude of a workingimplement, and a control unit for determining based on a detectionsignal from the attitude detecting means whether the working implementcomes within a predetermined zone around the operator's seat portion.When it is determined that the working implement comes within thepredetermined zone around the operator's seat portion, the control unitoutputs a control command to a hydraulic circuit, for a hydraulicactuator associated with the working implement, so that the workingimplement is stopped.

One known example of such a related art device is shown in FIG. 9. Inthe example, solenoid proportional pressure reducing valves 49A, 49B,which operate in accordance with a command from a control unit, areprovided between a pilot-operated control valve 46 for controlling thesupply of pressurized oil to a hydraulic actuator 45, e.g., a boomcylinder, and pilot valves 48A, 48B for delivering pilot pressurized oilupon manipulation of a control member 47. When the working implement ispositioned away from the operator's seat portion, the solenoidproportional pressure reducing valves 49A, 49B are opened to allow thesupply of the pilot pressurized oil to the control valve 46. On thecontrary, when the working implement comes close to the operator's seatportion, the solenoid proportional pressure reducing valves 49A, 49B areclosed to cut off the supply of the pilot pressurized oil to the controlvalve 46, thereby stopping the working implement.

The above prior art however has a problem. Because the solenoidproportional pressure reducing valves are closed to stop the workingimplement when the working implement comes close to the operator's seatportion, as described above, the working implement is stopped during theoperation and the working efficiency is reduced. The invention intendsto overcome such a problem.

SUMMARY OF THE INVENTION

In view of the state of art set forth above, the invention has been madewith the object of solving the above problem. In a hydraulic controlcircuit for a working machine, comprising a hydraulic actuator operatedto move a working implement, and a pilot-operated control valve forcontrolling the supply of pressurized oil to the hydraulic actuator, thehydraulic control circuit includes a control valve for controlling thesupply of pilot pressurized oil to the pilot-operated control valve inaccordance with a command from a control unit, a pilot valve fordelivering the pilot pressurized oil to the control valve in accordancewith manipulation of a control member, a pilot pump oil line capable ofsupplying the pilot pressurized oil to the control valve from a pilotoil pressure source without passing the pilot valve, and a selectorvalve for supplying the pilot pressurized oil delivered from the pilotvalve to the control valve when the control member is manipulated, andsupplying the pilot pressurized oil from the pilot pump oil line to thecontrol valve when the control member is not manipulated, the controlunit including determining means for determining whether the workingimplement has entered a preset interference prevention area based oninput signals from attitude detecting means for detecting an attitude ofthe working implement, and interference prevention control means foroutputting a control command to the control valve, causing the pilotpressurized oil to be supplied to the pilot-operated control valve inthe direction to move the working implement away from the interferenceprevention area, when the determining means determines that the workingimplement has entered the preset interference prevention area.

In the above hydraulic control circuit, the hydraulic actuator formoving the working implement comprises a boom up-and-down movingcylinder for vertically swinging an offset type boom which is swingablein the up-and-down and left-and-right directions, a boom left-and-rightmoving cylinder for swinging the boom to the left and right, and a stickcylinder for swinging a stick back and forth which is supported to afore end of the boom to be swingable in the back-and-forth direction;the control valve, the pilot valve, the pilot pump oil line and theselector valve are provided in an oil line for supplying the pilotpressurized oil to the pilot-operated control valve for the stickcylinder in the direction to move the stick away from the interferenceprevention area; and the control valve and the pilot valve are providedin each oil line for supplying the pilot pressurized oil to each of thepilot-operated control valves for the boom up-and-down moving cylinder,the boom left-and-right moving cylinder, and the stick cylinder in thedirection to move the boom or the stick closer toward the interferenceprevention area.

Also, according to a second aspect of the invention, in a hydrauliccontrol circuit for a working machine comprising first and secondhydraulic actuators for operating a working implement, and first andsecond pilot-operated control valves for respectively controlling supplyof pressurized oil to the hydraulic actuators, the hydraulic controlcircuit includes interference prevention control means for preventingthe working implement from entering a interference prevention area setin advance to avoid interference between a body of the working machineand the working implement; and the interference prevention control meansincludes a mechanism for operating the first hydraulic actuator in thedirection away from the interference prevention area, thereby continuingoperation of the second hydraulic actuator while the working implementis prevented from entering the interference prevention area, when it isdetermined at least in a state of the second hydraulic actuator beingoperated that the working implement has reached the interferenceprevention area, the mechanism including valve means for switching overthe circuit such that pilot pressurized oil for operating the secondhydraulic actuator is also supplied to a pilot oil line for operatingthe first hydraulic actuator in the direction away from the interferenceprevention area.

In the above hydraulic control circuit, the hydraulic control circuitmay include first and second approaching-side pilot oil lines forsupplying the pilot pressurized oil respectively to the first and secondpilot-operated control valves in the direction of moving the workingimplement to approach the interference prevention area, first and secondaway-side pilot oil lines for supplying the pilot pressurized oilrespectively to the first and second pilot-operated control valves inthe direction of moving the working implement away from the interferenceprevention area, and first and second approaching- and away-side pilotvalves for outputting the pilot pressurized oil respectively to thefirst and second approaching- and away-side pilot oil lines inaccordance with manipulation of first and second control members, and acontrol valve for opening and closing one of the pilot oil lines inaccordance with a command from the interference prevention control meansmay be provided at least in the first approaching-side pilot line.

In the above hydraulic control circuit, when the second hydraulicactuator is provided as plurality of facilitators, a secondpilot-operated control valve, a second approaching- and away-side pilotoil lines, a second approaching- and away-side pilot valves may beprovided for each of the hydraulic actuators, and the pilot pressurizedoil delivered from the second approaching-side pilot valve may besupplied to the valve means after being joined with other pilotpressurized oil through a shuttle valve for selecting the pilotpressurized oil on the higher pressure side.

Further, the valve means may comprise a selector valve for switchingover the circuit such that when the pilot pressurized oil is deliveredfrom the first away-side pilot valve, the delivered pilot pressurizedoil is supplied to the first away-side pilot oil line, and when thepilot pressurized oil is not delivered from the first away-side pilotvalve, the pilot pressurized oil delivered from the secondapproaching-side pilot valve is supplied to the first away-side pilotoil line, and a control valve for opening and closing the firstapproaching-side pilot oil line in accordance with a command from theinterference prevention control means.

Moreover, the valve means may comprise a control valve for outputtingthe pilot pressurized oil delivered from the second approaching-sidepilot valve in accordance with a command from the interferenceprevention control means, and a shuttle valve for selecting one on thehigher pressure side of the pilot pressurized oil delivered from thecontrol valve and the pilot pressurized oil delivered from the firstaway-side pilot valve and supplying the selected pilot pressurized oilto the first away-side pilot oil line.

In the above features, the working machine may be a hydraulic shovelincluding, as the second hydraulic actuator, a boom up-and-down movingcylinder for vertically swinging an offset type boom which is swingablein the up-and-down and left-and-right directions, and an offset cylinderfor swinging the boom to the left and right, and including, as the firsthydraulic actuator, a stick cylinder for swinging a stick back and forthwhich is supported to a fore end of the boom to be swingable in theback-and-forth direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a hydraulic shovel;

FIG. 2 is a plan view of a hydraulic shovel, showing a state where afront boom is swung to the left and right;

FIG. 3 is a hydraulic control circuit diagram for a hydraulic actuatoraccording to a first embodiment;

FIG. 4 is a block diagram showing control procedures for interferenceprevention control;

FIG. 5 is a table showing control commands for the interferenceprevention control;

FIGS. 6(A) and (B) show respectively the case where the stick angle isan angle of elevation and the case where the stick angle is an angle ofdeclination;

FIG. 7 is a hydraulic control circuit diagram for a hydraulic actuatoraccording to a second embodiment;

FIG. 8 is a hydraulic control circuit diagram for a hydraulic actuatoraccording to a third embodiment, and

FIG. 9 is a hydraulic control circuit diagram for a related arthydraulic actuator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A first embodiment of the invention will be first described withreference to FIGS. 1 to 6. In FIGS. 1 and 2, numeral 1 denotes an offsettype hydraulic shovel having a similar basic structure as theconventional hydraulic shovel. The hydraulic shovel 1 is made up ofvarious components, such as a traveling undercarriage 2, an upperswiveling body 3, a cab 4, and a working implement 5. The workingimplement 5 comprises a rear boom 6 supported at its base end to theupper swiveling body 3 to be swingable vertically, a front boom 7supported to a fore end of the rear boom 6 to be swingable to the leftand right, a stick 8 supported to a fore end of the front boom 7 to beswingable in the left-and-right and the back-and-forth directions, and abucket 9 supported to a fore end of the stick 8 to be swingable back andforth. For swinging those members, the working implement 5 furthercomprises a boom cylinder (corresponding to a boom up-and-down movingcylinder in the invention) 10, an offset cylinder (corresponding to aboom left-and-right moving cylinder in the invention) 11, a stickcylinder 12, and a bucket cylinder 13. In this embodiment, the cab 4 isprovided on the left side of the upper swiveling body 3.

The rear boom 6 is constructed to move down when the boom cylinder 10 iscontracted, and to move up when the boom cylinder 10 is extended. Also,the front boom 7 is constructed to move to the left, i.e., in thedirection toward the cab 4, when the offset cylinder 11 is contracted,and to move to the right when the offset cylinder 11 is extended.Furthermore, the stick 8 is constructed to swing (stick-in) toward themachine body when the stick cylinder 12 is extended, and to swing(stick-out) away from the machine body and move up when the stickcylinder 12 is contracted.

Control of the supply of pressurized oil to the cylinders 10-13 will bedescribed with reference to a hydraulic control circuit diagram shown inFIG. 3. In FIG. 3, numeral 14 denotes a main pump, 15 denotes a pilotpump, 16 denotes an oil tank, and 17-20 denote control valves for theboom, the offset, the stick and the bucket, respectively. The controlvalves 17-20 comprise pilot-operated 3-position selector valves providedwith contraction-side pilot ports 17 a-20 a and extension-side pilotports 17 b-20 b, respectively.

When no pilot pressurized oil is supplied to any of the pilot ports 17a-20 a and 17 b-20 b, the control valves 17-20 are held in neutralpositions N where the supply of the pressurized oil to the correspondingcylinders 10-13 is stopped. When the pilot pressurized oil is suppliedto the contraction-side pilot ports 17 a-20 a, the control valves 17-20are shifted to contraction-side positions X where the pressurized oilfrom the main pump 14 is supplied to contraction-side oil chambers ofthe cylinders 10-13. Also, when the pilot pressurized oil is supplied tothe extension-side pilot ports 17 b-20 b, the control valves 17-20 areshifted to extension-side positions Y where the pressurized oil from themain pump 14 is supplied to extension-side oil chambers of the cylinders10-13.

Numerals 21-24 denote respectively boom, offset, stick and bucket pilotvalves for supplying pilot pressurized oil to the pilot ports 17 a-20 a,17 b-20 b of the control valves 17-20 in accordance with themanipulation of the control members (not shown). The pilot valves 21-24comprise contraction-side pilot valves 21A-24A and extension-side pilotvalves 21B-24B, respectively.

The pilot valves 21-24 are structured as follows. When the correspondingcontrol members are in neutral positions (i.e., they are notmanipulated), pump ports 21 a-24 a connected to the pilot pump 15 areclosed, and tank ports 21 b-24 b connected to the oil tank 16 are incommunication with output ports 21 c-24 c. When the control members aremanipulated to the contraction side and the extension side, the outputports 21 c-24 c of the pilot valves 21A-24A or 21B-24B, on the side towhich the control members are manipulated, are in communication with thepump ports 21 a-24 a, whereupon the pilot pressurized oil is deliveredthrough the output ports 21 c-24 c at pressures corresponding to theamount by which the control members are manipulated.

Further, in FIG. 3, numerals 25, 26, 27 denote respectively a swivelmotor, a swivel control valve, and a swivel pilot valve whichcooperatively turn the upper swiveling body 3.

The solenoid proportional pressure reducing valves 28, 29, 30, 31 forthe boom contraction side, the boom extension side, the offsetcontraction side and the stick extension side are provided respectivelyin a boom contraction-side pilot oil line connecting the boomcontraction-side pilot valve 21A and the boom control valvecontraction-side pilot port 17 a, a boom extension-side pilot oil lineconnecting the boom extension-side pilot valve 21B and the boom controlvalve extension-side pilot port 17 b, in an offset contraction-sidepilot oil line connecting the offset contraction-side pilot valve 22Aand the offset control valve contraction-side pilot port 18 a, and astick extension-side pilot oil line connecting the stick extension-sidepilot valve 23B and the stick control valve extension-side pilot port 19b. Because each of the solenoid proportional pressure reducing valves28, 29, 30, 31 have a similar structure, the solenoid proportionalpressure reducing valve 28 on the boom extension side will, by way ofexample, be described. The solenoid proportional pressure reducing valve28 has first to third ports 28 a, 28 b, 28 c and a solenoid 28 d. Thefirst port 28 a is connected to the oil tank 16, the second port 28 b isconnected to the output port 21 c of the boom contraction-side pilotvalve 21A, and the third port 28 c is connected to the contraction-sidepilot port 17 a of the boom control valve 17.

When the solenoid 28 d is not excited, the solenoid proportionalpressure reducing valve 28 opens a valve passage communicating the firstport 28 a and the third port 28 c, and closes the second port 28 b,thereby draining the oil from the contraction-side pilot port 17 a tothe oil tank 16. When the solenoid 28 d is excited in accordance with anoperating command from a control unit 32 (described later), an outputvalve passage communicating the second port 28 b and the third port 28 cis opened. Upon the above output valve passage being opened, the pilotpressurized oil from the pilot valve output port 21 c is delivered tothe control valve contraction-side pilot port 17 a. The output pressureis increased and decreased in accordance with a control commandoutputted to an excitation circuit of the solenoid 28 d from the controlunit 32.

On the other hand, a selector valve 33 and a solenoid proportionalpressure reducing valve 34 on the stick contraction side are provided ina stick contraction-side pilot oil line connecting the stickcontraction-side pilot valve 23A and the stick control valvecontraction-side pilot port 19 a.

A selector valve 33 is a 5-port, 2-position selector valve having afirst port 33 a connected to the oil tank 16, a second port 33 bconnected to an output port 23 c of the stick contraction-side pilotvalve 23A, a third port 33 c connected to a pilot pump oil line P, afourth port 33 d connected to a first port 34 a of the solenoidproportional pressure reducing valve 34 on the stick contraction side,and a fifth port 33 e connected to a second port 34 b of the solenoidproportional pressure reducing valve 34 on the stick contraction side.Here, the pilot pump oil line P is an oil line extending from a pointupstream of the stick pilot valve 23 to the selector valve 33. Throughthe pilot pump oil line P, the pressurized oil from the pilot pump 15 issupplied to the selector valve 33 while bypassing the stick pilot valve23.

The selector valve 33 further has a pilot port 33 f. The pilot port 33 fis connected to a pilot oil line connecting the stick contraction-sidepilot valve output port 23 c and the selector valve second port 33 b.When the pilot pressurized oil is delivered from the stickcontraction-side pilot valve 23A, the pilot pressurized oil is suppliedto the pilot port 33 f as well.

In a state where the pilot pressurized oil is not supplied to the pilotport 33 f, the selector valve 33 is in a first position X at which thefirst port 33 a is closed by an urging force of a spring 33 g, a valvepassage extending from the third port 33 c to the fifth port 33 e isopened, and a valve passage extending from the fourth port 33 d to thesecond port 33 b is opened. Therefore, the pilot pressurized oil fromthe pilot pump line P can be supplied to the solenoid proportionalpressure-reducing-valve second port 34 b, and the oil from the solenoidproportional pressure-reducing-valve first port 34 a can be drained tothe oil tank 16 through the pilot valve 23A.

On the contrary, when the pilot pressurized oil is supplied to the pilotport 33 f, the selector valve 33 is shifted to a second position Y atwhich the third port 33 c is closed, a valve passage extending from thesecond port 33 b to the fifth port 33 e is opened, and a valve passageextending from the fourth port 33 d to the first port 33 a is opened.Therefore, the pilot pressurized oil from the pilot valve output port 23c can be supplied to the solenoid proportional pressure-reducing-valvesecond port 34 b, and the oil from the solenoid proportionalpressure-reducing-valve first port 34 a can be drained to the oil tank16.

Also, the solenoid proportional pressure reducing valve 34 on the stickcontraction side has a similar structure to that of the solenoidproportional pressure reducing valves 28, 29, 30, 31 described above,and operates to increase and decrease the output pressure in accordancewith a control command from the control unit 32. The solenoidproportional pressure reducing valve 34 on the stick contraction sidehas the first port 34 a connected to the fourth port 33 d of theselector valve 33, the second port 34 b connected to the selector valvefifth port 33 e, and a third port 34 c connected to the contraction-sidepilot port 19 a of the stick control valve 19, respectively.

In a state where a solenoid 34 d is not excited, the solenoidproportional pressure reducing valve 34 on the stick contraction sideopens a valve passage communicating the first port 34 a and the thirdport 34 c, and closes the second port 34 b, thereby draining the oilfrom the contraction-side pilot port 19 a to the oil tank 16. When thesolenoid 34 d is excited in accordance with an operating command fromthe control unit 32, an output valve passage communicating the secondport 34 b and the third port 34 c is opened. Upon the above output valvepassage being opened, the pilot pressurized oil from the pilot pump oilline P having passed the selector valve 33 in the first position X orthe pilot pressurized oil from the pilot valve 23A having passed theselector valve 33 in the second position Y is delivered to the controlvalve contraction-side pilot port 19 a.

Further, a locking solenoid valve 35 is disposed on the primary(upstream) side of the pump ports 21 a-24 a of the pilot valves 21-24and the third port 33 c of the selector valve 33. Upon a lock controlmember (not shown) being manipulated by an operator, the lockingsolenoid valve 35 is shifted between an unlock position X at which thepilot pressurized oil from the pilot pump 15 is delivered to the pilotvalves 21-24 and the selector valve 33, and a lock position Y at whichthe pilot pressurized oil is not delivered.

The control unit 32 comprises a microcomputer that receives signals froma boom angle sensor 36 for detecting a relative angle of the rear boom 6to the upper swiveling body 3, an offset angle sensor 37 for detecting arelative angle of the front boom 7 to the rear boom 6, a stick anglesensor 38 for detecting a relative angle of the stick 8 to the frontboom 7, a pressure sensor 39A on the boom contraction side for detectingthat the pilot pressurized oil is delivered from the boomcontraction-side pilot valve 21A, as well as other pressure sensors 39B,40A, 41A, 41B on the boom extension side, the offset contraction side,the stick contraction side, and the stick extension side forrespectively detecting that the pilot pressurized oil is delivered fromthe pilot valves 21B, 22A, 23A, 23B on the boom extension side, theoffset contraction side, the stick contraction side, and the stickextension side. Based on the input signals, the control unit 32 outputscontrol commands to the solenoid proportional pressure reducing valves28, 29, 30, 34, 31 on the boom contraction side, the boom extensionside, the offset contraction side, the stick contraction side, and thestick extension side, etc.

Incidentally, solenoid proportional pressure reducing valves, which areoperated in accordance with commands from the control unit 32, are notprovided in a pilot oil line connecting the offset extension-side pilotvalve 22B and the offset control valve extension-side pilot port 18 b,in an bucket contraction-side pilot oil line connecting the bucketcontraction-side pilot valve 24A and the bucket control valvecontraction-side pilot port 20 a, and a bucket extension-side pilot oilline connecting the bucket extension-side pilot valve 24B and the bucketcontrol valve extension-side pilot port 20 b. Upon the control membersbeing manipulated, therefore, the pilot pressurized oil delivered fromthe pilot valves 22B, 24A, 24B is directly supplied to the pilot ports18 b, 20 a, 20 b. In other words, the operations of rightward offset andthe bucket 9 are always performed as per the manipulations of thecontrol members without undergoing a later-described interferenceprevention control made by the control unit 32.

Next, the interference prevention control made by the control unit 32will be described with reference to a block diagram shown in FIG. 4. Thecontrol unit 32 first computes an attitude (position) of the workingimplement 5 by an attitude computing module 42 based on the detectionsignals from the boom angle sensor 36, the offset angle sensor 37, andthe stick angle sensor 38. A memory 32 a in the control unit 32 storesan interference prevention area (e.g., a zone within 300 mm from the cab4) H set to prevent the working implement 5 from entering the area andcoming close to the cab 4. The control unit 32 then executes comparisonoperation using a comparison operation module 43 for the attitude of theworking implement 5 computed by the attitude computing module 42 and theinterference prevention area H stored in the memory 32 a, and outputs anoperation result to an output signal computing module 44.

The signals from the pressure sensors 39A, 39B, 40A, 41A, 41B on theboom contraction side, the boom extension side, the offset contractionside, the stick contraction side, and the stick extension side,respectively, are also inputted to the output signal computing module44.

Based on the input signals from the comparison operation module 43 andthe pressure sensors 39A, 39B, 40A, 41A, 41B, the output signalcomputing module 44 outputs command signals to solenoid excitationcircuits of the solenoid proportional pressure reducing valves 28, 29,30, 34, 31 on the boom contraction side, the boom extension side, theoffset contraction side, the stick contraction side, and the stickextension side.

More specifically, when the comparison operation module 43 provides anoperation result indicating the working implement 5 is away from theinterference prevention area H by a distance not smaller than a certainrange set in advance, the output signal computing module 44 outputssolenoid excitation commands to the solenoid proportional pressurereducing valves 28, 29, 30, 34, 31 in the pilot oil lines where deliveryof the pilot pressurized oil is detected by the pressure sensors 39A,39B, 40A, 41A, 41B, causing the output valve passages to be fullyopened.

Therefore, when the pilot pressurized oil is delivered from the pilotvalves 21A, 21B, 22A, 23B on the boom contraction side, the boomextension side, the offset contraction side, and the stick extensionside upon manipulation of the control members, the delivered pilotpressurized oil is supplied as it is to the control valve pilot ports 17a, 17 b, 18 a, 19 b via the solenoid proportional pressure reducingvalves 28, 29, 30, 31 which are fully opened.

Also, while the selector valve 33 is provided in the stickcontraction-side pilot oil line, the selector valve 33 is shifted to thesecond position Y for supplying the pilot pressurized oil from the pilotvalve 23A to the solenoid proportional pressure reducing valve 34, asdescribed above, in the state where the pilot pressurized oil isdelivered from the stick contraction-side pilot valve 23A uponmanipulation of the control member. Therefore, when the pilotpressurized oil is delivered from the stick contraction-side pilot valve23A upon manipulation of the control member, the delivered pilotpressurized oil is supplied to the control valve pilot port 19 a via theselector valve 33 in the second position Y and the solenoid proportionalpressure reducing valve 33 which is fully opened.

Thus, when the working implement 5 is away from the interferenceprevention area H by the predetermined distance or more, the workingimplement 5 is operated as per the manipulation of the control member.

On the contrary, when the comparison operation module 43 provides as anoperation result that the working implement 5 is coming or has come intothe certain range set in advance with respect to the interferenceprevention area H, the output signal computing module 44 outputssolenoid excitation commands to the solenoid proportional pressurereducing valves 28, 29, 30, 34, 31 in the pilot oil lines where deliveryof the pilot pressurized oil is detected by the pressure sensors 39A,39B, 40A, 41A, 41B, causing the output valve passages to be opened. Inthis case, the opening degrees of the output valve passages of thesolenoid proportional pressure reducing valves 28, 29, 30, 34, 31 areadjusted so that the output pressures of the solenoid proportionalpressure reducing valves 28, 29, 30, 34, 31 become smaller as theworking implement 5 comes closer to the interference prevention area H.

Therefore, when the pilot pressurized oil is delivered from the pilotvalves 21A, 21B, 22A, 23A, 23B on the boom contraction side, the boomextension side, the offset contraction side, the stick contraction side,and the stick extension side upon manipulation of the control members,the delivered pilot pressurized oil is supplied to the control valvepilot ports 17 a, 17 b, 18 a, 19 a, 19 b while being reduced in pressureby the solenoid proportional pressure reducing valves 28, 29, 30, 34,31.

Thus, when the working implement 5 approaches the interferenceprevention area H within the predetermined distance, the operations ofboom-down, boom-up, stick-out, stick-in, and leftward offset areperformed at slowed down speeds.

Then, when the comparison operation module 43 provides as an operationresult the working implement 5 has reached an outer boundary line of theinterference prevention area H, the output signal computing module 44outputs control commands to the solenoid proportional pressure reducingvalves 28, 29, 30, 31, 34 based on a command control table shown in FIG.5. In this embodiment, two areas, i.e., an interference prevention areafor a cab front/side portion (a front portion and a right side portionof the cab) and an interference prevention area for a cab roof portion,are each set as the interference prevention area H. In these areas, thecontrol is executed separately.

FIG. 5 shows the relationship between the states of control membermanipulation and operating commands issued to the working implement 5.In this respect, the states of the control member manipulations for theboom-down, boom-up, stick-out, stick-in, and leftward-offset operationsare determined in accordance with inputting of the detection signalsfrom the pressure sensors 39A, 39B, 41A, 41B, 40A on the boomcontraction side, the boom extension side, the stick contraction side,the stick extension side, and the offset contraction side.

As to the operating commands for the boom-down, boom-up, stick-out, andleftward-offset operations, solenoid excitation commands are outputtedto the solenoid proportional pressure reducing valves 28, 29, 34, 30 onthe boom contraction side, the boom extension side, the stickcontraction side, and the offset contraction side, causing the outputvalve passages to be opened. Further, as to the operating commands tostop the boom-down, boom-up, stick-in, stick-out, and leftward-offsetoperations, solenoid non-excitation commands are outputted to thesolenoid proportional pressure reducing valves 28, 29, 31, 34, 30 on theboom contraction side, the boom extension side, the stick extensionside, the stick contraction side, and the offset contraction side,causing the output valve passages to be closed.

Here, the operating commands for the boom-down, boom-up, andleftward-offset operations are outputted in states where the boom-down,boom-up, and leftward-offset manipulations are performed. Accordingly,when the output valve passages of the solenoid proportional pressurereducing valves 28, 29, 30 are opened, the pilot pressurized oildelivered from the pilot valves 21A, 21B, 22A is supplied to the controlvalve pilot ports 17 a, 17 b, 18 a. On the other hand, the operatingcommand for the stick-out operation is outputted in a state where thestick-out manipulation is not performed, and hence the pilot pressurizedoil is not delivered from the pilot valve 23A. In the state where thepilot pressurized oil is not delivered from the pilot valve 23A,however, the selector valve 33 provided in the stick contraction-sidepilot oil line is in the first position X, as described above.Accordingly, the pilot pressurized oil from the pilot pump oil line P issupplied to the control valve pilot port 19 a via the selector valve 33in the first position X and the solenoid proportional pressure reducingvalve 34.

A description will be first made on the control to be executed when theworking implement 5 has reached the outer boundary line of theinterference prevention area H given by the front/side-portioninterference prevention area. When the boom-down manipulation is solelyperformed, the operating commands for the boom-down and stick-outoperations are outputted. As a result, the boom-down operation can becontinued while the stick 8 is moved out so as to avoid the workingimplement 5 from entering the interference prevention area H. In thiscase, the working implement 5 is moved down substantially along theouter boundary line of the interference prevention area H.

When the stick-in manipulation is solely performed, the operatingcommand to stop the stick-in operation is outputted. Also, when theleftward-offset manipulation is solely performed, the operating commandto stop the leftward offset operation is outputted.

When the boom-down and stick-in manipulations are performed in acombined manner, the operating commands for the boom-down and stick-outmanipulations are outputted. Also, when the boom-down andleftward-offset manipulations are performed in a combined manner, theoperating commands for the boom-down, stick-out and leftward-offsetoperations are outputted. Further, when the stick-in and leftward-offsetmanipulations are performed in a combined manner, the operating commandsfor the stick-out and leftward-offset operations are outputted.Moreover, when the boom-down, stick-in and leftward-offset manipulationsare performed in a combined manner, the operating commands for theboom-down, stick-out and leftward-offset operations are outputted. As aresult, the boom-down and leftward-offset operations can be continuedwhile the stick 8 is moved out so as to avoid the working implement 5from entering the interference prevention area H. In this case, theworking implement 5 is moved substantially along the outer boundary lineof the interference prevention area H.

When the boom-up manipulation is solely performed, the operatingcommands for the boom-up and stick-out operations are outputted. As aresult, the boom-up operation can be continued while the stick 8 ismoved out so as to avoid the working implement 5 from entering theinterference prevention area H. In this case, the working implement 5 ismoved substantially along the outer boundary line of the interferenceprevention area H.

When the boom-up and stick-in manipulations are performed in a combinedmanner, the operating commands for the boom-up and stick-out operationsare outputted. Also, when the boom-up and leftward-offset manipulationsare performed in a combined manner, the operating commands for theboom-up, stick-out and leftward-offset operations are outputted.Further, when the boom-up, stick-in and leftward-offset manipulationsare performed in a combined manner, the operating commands for theboom-up, stick-out and leftward-offset operations are outputted. As aresult, the boom-up and leftward-offset operations can be continuedwhile the stick 8 is moved out so as to avoid the working implement 5from entering the interference prevention area H. In this case, theworking implement 5 is moved substantially along the outer boundary lineof the interference prevention area H.

In the control relating to the front/side-portion interferenceprevention area, when the stick-out manipulation is performed solely orin combination with any of the above-mentioned manipulations (it is amatter of course that the stick-out manipulation and the stick-inmanipulation are never performed at the same time), the operatingcommand for the stick-out operation is outputted solely or incombination with any of the above-mentioned operating commands.

Next, a description will be made of the control to be executed when theworking implement 5 has reached the outer boundary line of theinterference prevention area H given by the roof-portion interferenceprevention area. When the boom-down manipulation is solely performed,the operating command to stop the boom-down operation is outputted. Whenthe stick-in manipulation is solely performed, the operating command tostop the stick-in operation is outputted. When the stick-outmanipulation is solely performed, the operating command to stop thestick-out operation is outputted.

As to the operating command outputted when the boom-down manipulation issolely performed, the setting may be changed such that the operatingcommands for the boom-down and stick-out operations are outputted oncondition that the angle of the stick 8 is an angle of elevation, aswith when the boom-down and stick-in manipulations are performed in acombined manner as described later. In such a case, the boom-downoperation can be continued while the stick 8 is moved out so as to avoidthe working implement 5 from entering the interference prevention areaH.

When the boom-down and stick-in manipulations are performed in acombined manner, the operating commands for the boom-down and stick-outoperations or the operating commands to stop the boom-down and stick-inoperations are outputted depending on the attitude of the stick 8.Specifically, when the angle of the stick 8 is an angle of elevationwith respect to a vertical line L passing the pivotal fulcrum of thestick 8 as shown in FIG. 6(A), the operating commands for the boom-downand stick-out operations are outputted. As a result, the boom-downoperation can be continued while the stick 8 is moved out so as to avoidthe working implement 5 from entering the interference prevention areaH. In this case, the working implement 5 is moved substantially alongthe outer boundary line of the interference prevention area H. Also,when the angle of the stick 8 is an angle of declination with respect tothe vertical line L passing the pivotal fulcrum of the stick 8 as shownin FIG. 6(B), the operating commands to stop the boom-down and stick-inoperations are outputted.

When the boom-down and stick-out manipulations are performed in acombined manner, the operating commands to stop the boom-down andstick-out operations are outputted.

Furthermore, in this control regarding the roof portion interferenceprevention area, when the boom-up manipulation is performed, theoperating command for the boom-up operation is outputted, and when theleftward-offset manipulation is performed, the operating command for theleftward-offset operation is outputted. However, when the boom-up andleftward-offset manipulations are performed in combination with any ofthe above-mentioned manipulations (it is a matter of course that theboom-up manipulation and the boom-down manipulation are never performedat the same time), the operating commands for the boom-up andleftward-offset operations are outputted in combination with any of theabove-mentioned operations.

Additionally, in the control regarding any of the front/side-portioninterference prevention areas and the roof-portion interferenceprevention area, the operations of rightward offset and the bucket 9 areperformed as per the manipulations of the control members because thoseoperations are not subject to the interference prevention control asdescribed above.

With the hydraulic control circuit thus structured, the workingimplement 5 is controlled as described above. Specifically, when theworking implement 5 is away from the interference prevention area H bythe predetermined distance or more, the working implement 5 is operatedas per the manipulation of the control member. However, when the workingimplement 5 approaches the interference prevention area H within thepredetermined distance, the working implement 5 is automatically sloweddown. Upon reaching the interference prevention area H, depending on thestates of control member manipulation and the attitude of the workingimplement 5, the working implement 5 is automatically stopped, or thestick 8 is automatically moved out so that the up-and-down andleftward-offset operations of the boom 3 can be continued while avoidingthe working implement 5 from entering the interference prevention areaH.

As a result, when the working implement 5 reaches the interferenceprevention area H during the boom-down manipulation, for example, thestick 8 is automatically moved out and the operation of moving the boom6 down can be continued while avoiding the interference prevention areaH. Thus, the operation is no longer suspended as it was in the priorart. Therefore, working efficiency is improved.

In addition, since the operation can be continued while avoiding theinterference prevention area H just by automatically moving the stick 8out, a circuit for automatically contracting a cylinder is required tobe built in only the circuit for the stick cylinder 12 among thehydraulic actuators provided on the working implement 5. Thiscontributes to simplifying the circuit and holding down any costincreases.

Such a circuit for automatically contracting a cylinder, which is to bebuilt in the circuit for the stick cylinder 12, is built in the stickcontraction-side pilot oil line. In this regard, one of the pilotpressurized oil delivered from the pilot valve 23A and the pilotpressurized oil supplied through the pilot pump oil line P is selectedby the selector valve 33, and the selected pilot pressurized oil issupplied to the solenoid proportional pressure reducing valve 34 whichis operated in accordance with a command from the control unit 32. It istherefore only required to provide the selector valve 33 and the pilotpump oil line P in the conventional circuit for automatically stoppingthe cylinder with no need of adding an expensive solenoid proportionalpressure reducing valve. This further contributes to holding down anyincrease in costs.

In the above first embodiment, the selector valve 33 is constructed toshift from the first position X to the second position Y upon the pilotpressurized oil being supplied to the pilot port 33 f. However, theselector valve may comprise a solenoid valve shifting from a firstposition to a second position in accordance with a solenoid excitationcommand from the control unit, and the control unit may output thesolenoid excitation command for shifting the selector valve to thesecond position when the detection signal from the stickcontraction-side pressure sensor is inputted to the control unit.

Next, FIG. 7 shows a hydraulic control circuit diagram according to asecond embodiment. In the second embodiment, the same reference numeralsdenote the same components as in the first embodiment and a detaileddescription thereof is omitted here. Components denoted by differentreference line numerals and oil lines related to them will be describedin detail. In the second embodiment a stick cylinder 12 corresponds tothe first hydraulic actuator of the invention and a boom cylinder 10 andan offset cylinder correspond to the second hydraulic actuator of theinvention.

First, a third port 33 c of a selector valve 33 provided in a stickcontraction-side pilot oil line is connected to an avoidance pilot oilline 50 described later. Then, in a state where the pilot pressurizedoil is not supplied to a pilot port 33 f, the selector valve 33 is in afirst position X at which a first port 33 a is closed by an urging forceof a spring 33 g, a valve passage extending from the third port 33 c toa fifth port 33 e is opened, and a valve passage extending from a fourthport 33 d to a second port 33 b is opened. Therefore, the pilotpressurized oil from the avoidance pilot oil line 50 can be supplied toa solenoid proportional pressure-reducing-valve second port 34 b, andthe oil from a solenoid proportional pressure-reducing-valve first port34 a can be drained to an oil tank 16 through a pilot valve 23A. As withthe first embodiment, when the pilot pressurized oil is supplied to thepilot port 33 f, the selector valve 33 is shifted to a second position Yat which the third port 33 c is closed, a valve passage extending fromthe second port 33 b to the fifth port 33 e is opened, and a valvepassage extending from the fourth port 33 d to the first port 33 a isopened. Therefore, the pilot pressurized oil from a pilot valve outputport 23 c can be supplied to the solenoid proportionalpressure-reducing-valve second port 34 b, and the oil from the solenoidproportional pressure-reducing-valve first port 34 a can be drained tothe oil tank 16.

Also, as with the first embodiment, in a state where a solenoid 34 d isnot excited, the solenoid proportional pressure reducing valve 34provided on the stick contraction side opens a valve passagecommunicating the first port 34 a and the third port 34 c, and closesthe second port 34 b, thereby draining the oil from the contractionsidepilot port 19 a to the oil tank 16. When the solenoid 34 d is excited inaccordance with an operating command from a control unit 32, an outputvalve passage communicating the second port 34 b and the third port 34 cis opened. Upon the above output valve passage being opened, the pilotpressurized oil from the avoidance pilot oil line 50 having passed theselector valve 33 in the first position X or the pilot pressurized oilfrom the pilot valve 23A having passed the selector valve 33 in thesecond position Y is delivered to a control valve contraction-side pilotport 19 a.

Here, the avoidance pilot oil line 50 is structured such that the pilotpressurized oil delivered from pilot valves 21A, 21B on the boomcontraction and extension sides and a pilot valve 22A on the offsetcontraction side is supplied to the selector valve 33 through first andsecond shuttle valves 51, 52.

More specifically, a boom contraction-side pilot branch oil line 53 isbranched from midway in an oil line connecting the boom contraction-sidepilot valve 21A and a solenoid proportional pressure reducing valve 28on the boom contraction side. Also, a boom extension-side pilot branchoil line 54 is branched from midway in an oil line connecting the boomextension-side pilot valve 21B and a solenoid proportional pressurereducing valve 29 on the boom extension side. Further, an offsetcontraction-side pilot branch oil line 55 is branched from midway in anoil line connecting the offset contraction-side pilot valve 22A and asolenoid proportional pressure reducing valve 30 on the offsetcontraction side.

The boom contraction- and extension-side pilot branch oil lines 53, 54are connected respectively to inlet-side first and second ports 51 a, 51b of the first shuttle valve 51, whereas an inlet-side first port 52 aof the second shuttle valve 52 is connected to an outlet-side port 51 cof the first shuttle valve 51. Further, the offset contraction-sidepilot branch oil line 55 is connected to an inlet-side second port 52 bof the second shuttle valve 52, and an outlet-side port 52 c of thesecond shuttle valve 52 is connected to the avoidance pilot oil line 50.Accordingly, when the pilot pressurized oil is delivered from the boomcontraction- or extension-side pilot valve 21A, 21B, the delivered pilotpressurized oil is supplied to the avoidance pilot oil line 50 via theboom contraction- or extension-side pilot branch oil line 53, 54, thefirst shuttle valve 51, and the second shuttle valve 52. Also, when thepilot pressurized oil is delivered from the offset contraction-sidepilot valve 22A, the delivered pilot pressurized oil is supplied to theavoidance pilot oil line 50 via the offset contraction-side pilot branchoil line 55 and the second shuttle valve 52. Incidentally, when thepilot pressurized oil is delivered from either of the boom contraction-or extension-side pilot valves 21A, 21B and the offset contraction-sidepilot valve 22A, the pilot pressurized oil on the higher pressure sideis supplied to the avoidance pilot oil line 50.

Furthermore, numeral 35 denotes a locking solenoid valve which isdisposed on the primary (upstream) side of the pilot valves 21-24, 27.Upon a lock control member (not shown) being manipulated by an operator,the locking solenoid valve 35 is shifted between an unlock position X atwhich the pilot pressurized oil from the pilot pump 15 is delivered tothe pilot valves 21-14, 27, and a lock position Y at which the pilotpressurized oil is not delivered.

On the other hand, an output signal computing module 44, providedsimilarly to the first embodiment, outputs command signals to solenoidexcitation circuits of the solenoid proportional pressure reducingvalves 28, 29, 30, 34, 31 on the boom contraction side, the boomextension side, the offset contraction side, the stick contraction side,and the stick extension side based on input signals from a comparisonoperation module 43 and pressure sensors 39A, 39B, 40A, 41A, 41B.

More specifically, when the comparison operation module 43 provides suchan operation result that the working implement 5 is away from theinterference prevention area H by a distance not smaller than a certainrange set in advance, the output signal computing module 44 outputssolenoid excitation commands to the solenoid proportional pressurereducing valves 28, 29, 30, 34, 31 in pilot oil lines where delivery ofthe pilot pressurized oil is detected by the pressure sensors 39A, 39B,40A, 41A, 41B, causing the output valve passages to be fully opened.

Therefore, when the pilot pressurized oil is delivered from the pilotvalves 21A, 21B, 22A, 23B on the boom contraction side, the boomextension side, the offset contraction side, and the stick extensionside upon manipulations of the control members, the delivered pilotpressurized oil is supplied as it is to control valve pilot ports 17 a,17 b, 18 a, 19 b via the solenoid proportional pressure reducing valves28, 29, 30, 31 which are fully opened.

Also, while the selector valve 33 is provided in the stickcontraction-side pilot oil line, the selector valve 33 is shifted to thesecond position Y for supplying the pilot pressurized oil from the pilotvalve 23A to the solenoid proportional pressure reducing valve 34, asdescribed above, in the state where the pilot pressurized oil isdelivered from the stick contraction-side pilot valve 23A uponmanipulation of the control member. Therefore, when the pilotpressurized oil is delivered from the stick contraction-side pilot valve23A upon manipulation of the control member, the delivered pilotpressurized oil is supplied to the control valve pilot port 19 a via theselector valve 33 in the second position Y and the solenoid proportionalpressure reducing valve 33 which is fully opened.

Thus, when the working implement 5 is away from the interferenceprevention area H by a predetermined distance or more, the workingimplement 5 is operated as per the manipulation of the control member.

On the contrary, when the comparison operation module 43 provides suchan operation result that the working implement 5 comes into the certainrange set in advance with respect to the interference prevention area H,the output signal computing module 44 outputs solenoid excitationcommands to the solenoid proportional pressure reducing valves 28, 29,30, 34, 31 in the pilot oil lines where delivery of the pilotpressurized oil is detected by the pressure sensors 39A, 39B, 40A, 41A,41B, causing the output valve passages to be opened at adjusted openingdegrees. In this case, the opening degrees of the output valve passagesof the solenoid proportional pressure reducing valves 28, 29, 30, 34, 31are adjusted so that the output pressures of the solenoid proportionalpressure reducing valves 28, 29, 30, 34, 31 become smaller as theworking implement 5 comes closer to the interference prevention area H.

Therefore, when the pilot pressurized oil is delivered from the pilotvalves 21A, 21B, 22A, 23A, 23B on the boom contraction side, the boomextension side, the offset contraction side, the stick contraction side,and the stick extension side upon manipulation of the control members,the delivered pilot pressurized oil is supplied to the control valvepilot ports 17 a, 17 b, 18 a, 19 a, 19 b while being reduced in pressureby the solenoid proportional pressure reducing valves 28, 29, 30, 34,31.

Thus, when the working implement 5 approaches the interferenceprevention area H within the predetermined distance, the operations ofboom-down, boom-up, stick-out, stick-in, and leftward offset areperformed at slowed down speeds.

Then, when the comparison operation module 43 provides such an operationresult that the working implement 5 has reached an outer boundary lineof the interference prevention area H, the output signal computingmodule 44 outputs control commands to the solenoid proportional pressurereducing valves 28, 29, 30, 31, 34 based on the command control tableshown in FIG. 5. In this embodiment, two areas, i.e., an interferenceprevention area for a cab front/side portion (a front portion and aright side portion of the cab) and an interference prevention area for acab roof portion, are each set as the interference prevention area H. Inthese areas, the control is executed separately.

FIG. 5 shows the relationship between the states of control membermanipulation and operating commands issued to the working implement 5.In this respect, the states of control member manipulation for theboom-down, boom-up, stick-out, stick-in, and leftward-offset operationsare determined in accordance with inputting of the detection signalsfrom the pressure sensors 39A, 39B, 41A, 41B, 40A on the boomcontraction side, the boom extension side, the stick contraction side,the stick extension side, and the offset contraction side.

As to the operating commands for the boom-down, boom-up, stick-out, andleftward-offset operations, solenoid excitation commands are outputtedto the solenoid proportional pressure reducing valves 28, 29, 34, 30 onthe boom contraction side, the boom extension side, the stickcontraction side, and the offset contraction side, causing the outputvalve passages to be opened. Further, as to the operating commands tostop the boom-down, boom-up, stick-in, stick-out, and leftward-offsetoperations, solenoid non-excitation commands are outputted to thesolenoid proportional pressure reducing valves 28, 29, 31, 34, 30 on theboom contraction side, the boom extension side, the stick extensionside, the stick contraction side, and the offset contraction side,causing the output valve passages to be closed.

Here, the operating commands for the boom-down, boom-up, andleftward-offset operations are outputted in states where the boom-down,boom-up, and leftward-offset manipulations are performed. Accordingly,when the output valve passages of the solenoid proportional pressurereducing valves 28, 29, 30 are opened, the pilot pressurized oildelivered from the pilot valves 21A, 21B, 22A is supplied to the controlvalve pilot ports 17 a, 17 b, 18 a.

As described later, the operating command for the stick-out operation isoutputted not only in the case where the stick-out manipulation isperformed, but also in the case where the stick-out manipulation is notperformed. When the stick-out manipulation is performed, namely when thepilot pressurized oil is delivered from the stick contraction-side pilotvalve 23A, the selector valve 33 is, as described above, in the secondposition Y at which the pilot pressurized oil from the pilot valve 23Ais supplied to the solenoid proportional pressure reducing valve 34.Accordingly, the pilot pressurized oil from the stick contraction-sidepilot valve 23A is supplied to the stick control valve contraction-sidepilot port 19 a via the selector valve 33 in the second position Y andthe output valve passage of the solenoid proportional pressure reducingvalve 34.

On the other hand, when the operating command for the stick-outoperation is outputted in a state where the stick-out manipulation isnot performed, the boom-down, boom-up, and leftward-offset manipulationsare performed solely or in a combined manner, and the pilot pressurizedoil delivered from any of the pilot valves 21A, 21B, 22A on the boomcontraction side, the boom extension side, and the offset contractionside is supplied to the avoidance pilot oil line 50, as described later.At this time, since the pilot pressurized oil is not delivered from thestick contraction-side pilot valve 23A, the selector valve 33 is in thefirst position X where the pressurized oil in the avoidance pilot oilline 50 is supplied to the solenoid proportional pressure reducing valve34. Accordingly, the pilot pressurized oil delivered from any of thepilot valves 21A, 21B, 22A on the boom contraction side, the boomextension side, and the offset contraction side is supplied to the stickcontrol valve contraction-side pilot port 19 a via the selector valve 33in the first position X and the output valve passage of the solenoidproportional pressure reducing valve 34.

A description will be first made of the control to be executed when theworking implement 5 has reached the outer boundary line of theinterference prevention area H given by the front/side-portioninterference prevention area. When solely the boom-down manipulation isperformed, the operating commands for the boom-down and stick-outoperations are outputted. As a result, the boom-down operation can becontinued while the stick 8 is moved out so as to avoid the workingimplement 5 from entering the interference prevention area H. In thiscase, the working implement 5 is moved down substantially along theouter boundary line of the interference prevention area H.

When solely the stick-in manipulation is performed, the operatingcommand to stop the stick-in operation is outputted. Also, when only theleftward-offset manipulation is performed, the operating command to stopthe leftward offset operation is outputted. As a result, the workingimplement 5 is automatically stopped and prevented from entering theinterference prevention area H.

When the boom-down and stick-in manipulations are performed in acombined manner, the operating commands for the boom-down and stick-outmanipulations are outputted. Also, when the boom-down andleftward-offset manipulations are performed in a combined manner, theoperating commands for the boom-down, stick-out and leftward-offsetoperations are outputted. Further, when the stick-in and leftward-offsetmanipulations are performed in a combined manner, the operating commandsfor the stick-out and leftward-offset operations are outputted.Moreover, when the boom-down, stick-in and leftward-offset manipulationsare performed in a combined manner, the operating commands for theboom-down, stick-out and leftward-offset operations are outputted. As aresult, the boom-down and leftward-offset operations can be continuedwhile the stick 8 is moved out so as to prevent the working implement 5from entering the interference prevention area H. In this case, theworking implement 5 is moved substantially along the outer boundary lineof the interference prevention area H.

When only the boom-up manipulation is performed, the operating commandsfor the boom-up and stick-out operations are outputted. As a result, theboom-up operation can be continued while the stick 8 is moved out so asto avoid the working implement 5 from entering the interferenceprevention area H. In this case, the working implement 5 is movedsubstantially along the outer boundary line of the interferenceprevention area H.

When the boom-up and stick-in manipulations are performed in a combinedmanner, the operating commands for the boom-up and stick-out operationsare outputted. Also, when the boom-up and leftward-offset manipulationsare performed in a combined manner, the operating commands for theboom-up, stick-out and leftward-offset operations are outputted.Further, when the boom-up, stick-in and leftward-offset manipulationsare performed in a combined manner, the operating commands for theboom-up, stick-out and leftward-offset operations are outputted. As aresult, the boom-up and leftward-offset operations can be continuedwhile the stick 8 is moved out so as to prevent the working implement 5from entering the interference prevention area H. In this case, theworking implement 5 is moved substantially along the outer boundary lineof the interference prevention area H.

In the control with respect to the front/side-portion interferenceprevention area, although not shown in FIG. 5, when the stick-outmanipulation is performed solely or in combination with any of theabove-mentioned manipulations (it is a matter of course that thestick-out manipulation and the stick-in manipulation are never performedat the same time), the operating command for the stick-out operation isoutputted solely or in combination with any of the above-mentionedoperating commands.

Next, a description will be made of the control to be executed when theworking implement 5 has reached the outer boundary line of theinterference prevention area H given by the roof-portion interferenceprevention area. When solely the boom-down manipulation is performed,the operating command to stop the boom-down operation is outputted. Whenonly the stick-in manipulation is performed, the operating command tostop the stick-in operation is outputted. When only the stick-outmanipulation is performed, the operating command to stop the stick-outoperation is outputted. As a result, the working implement 5 isautomatically stopped and prevented from entering the interferenceprevention area H.

As to the operating command outputted when only the boom-downmanipulation is performed, the setting may be changed such that theoperating commands for the boom-down and stick-out operations areoutputted on condition that the angle of the stick 8 is an angle ofelevation, as with when the boom-down and stick-in manipulations areperformed in a combined manner as described later. In such a case, theboom-down operation can be continued while the stick 8 is moved out soas to avoid the working implement 5 from entering the interferenceprevention area H.

When the boom-down and stick-in manipulations are performed in acombined manner, the operating commands for the boom-down and stick-outoperations or the operating commands to stop the boom-down and stick-inoperations are outputted depending on the attitude of the stick 8.Specifically, when the angle of the stick 8 is an angle of elevationwith respect to a vertical line L passing the pivotal fulcrum of thestick 8 as shown in FIG. 6(A), the operating commands for the boom-downand stick-out operations are outputted. As a result, the boom-downoperation can be continued while the stick 8 is moved out so as to avoidthe working implement 5 from entering the interference prevention areaH.

In this case, the working implement 5 is moved substantially along theouter boundary line of the interference prevention area H. Also, whenthe angle of the stick 8 is an angle of declination with respect to thevertical line L passing the pivotal fulcrum of the stick 8 as shown inFIG. 6(B), the operating commands to stop the boom-down and stick-inoperations are outputted. As a result, the working implement 5 isautomatically stopped and is prevented from entering the interferenceprevention area H.

When the boom-down and stick-out manipulations are performed in acombined manner, the operating commands to stop the boom-down andstick-out operations are outputted. As a result, the working implement 5is automatically stopped and is prevented from entering the interferenceprevention area H.

Furthermore, in the control with respect to the roof portioninterference prevention area, although not shown in FIG. 5, when theboom-up manipulation is performed, the operating command for the boom-upoperation is outputted, and when the leftward-offset manipulation isperformed, the operating command for the leftward-offset operation isoutputted. However, when the boom-up and leftward-offset manipulationsare performed in combination with any of the above-mentionedmanipulations (it is a matter of course that the boom-up manipulationand the boom-down manipulation are never performed at the same time),the operating commands for the boom-up and leftward-offset operationsare outputted in combination with any of the above-mentioned operations.

Additionally, in the control with respect to any of thefront/side-portion interference prevention area and the roof-portioninterference prevention area, the operations of rightward offset and thebucket 9 are performed as per the manipulations of the control membersbecause those operations are not subject to the interference preventioncontrol as described above.

With the hydraulic control circuit thus structured, the workingimplement 5 is controlled as described above. Specifically, when theworking implement 5 is away from the interference prevention area H bythe predetermined distance or more, the working implement 5 is operatedas per the manipulation of the control member. However, when the workingimplement 5 approaches the interference prevention area H within thepredetermined distance, the working implement 5 is automatically sloweddown. Upon reaching the interference prevention area H, depending on thestates of control member manipulation and the attitude of the workingimplement 5, the working implement 5 is automatically stopped, or thestick 8 is automatically moved out so that the up-and-down andleftward-offset operations of the working implement 5, i.e., theoperation of a second actuator toward the interference prevention area,can be continued while precluding the working implement 5 from enteringthe interference prevention area H.

As a result, when the working implement 5 reaches the interferenceprevention area H during the boom-down manipulation, for example, thestick 8 is automatically moved out and the operation of moving the boom6 down can be continued while avoiding the interference prevention areaH. Thus, the operation is no longer suspended unlike the prior art andworking efficiency is improved.

In addition, since the operation can be continued while avoiding theinterference prevention area H just by automatically moving the stick 8out, a circuit for automatically contracting a cylinder is required tobe built in only the circuit for the stick cylinder 12 among thehydraulic actuators provided on the working implement 5. Thiscontributes to simplifying the circuit and holding down any increase incost. Further, as only the operation of moving the stick 8 out isautomatically performed, the interference avoiding operation issimplified and the operator can easily recognize the operation under thecontrol.

Moreover, the pilot pressurized oil supplied to the stick control valvecontraction-side pilot port 19 a for automatically moving the stick 8out is the pilot pressurized oil delivered from any of the pilot valves21A, 21B, 22A on the boom contraction side, the boom extension side, andthe offset contraction side upon execution of the manipulation for theboom-down, boom-up or leftward-offset operations. Accordingly, anadditional advantage is obtained in that even if the solenoidproportional pressure reducing valve 34 on the stick contraction sideshould malfunction due to a failure, or for any other reason, and thestick 8 should move out unintentionally, the unintentional moving-out ofthe stick 8 can be ceased by stopping the manipulations for theboom-down, boom-up and leftward-offset operations toward theinterference prevention area.

In the above second embodiment, the selector valve 33 is constructed toshift from the first position X to the second position Y upon the pilotpressurized oil being supplied to the pilot port 33 f. However, theselector valve 33 may comprise a solenoid valve shifting from a firstposition to a second position in accordance with a solenoid excitationcommand from the control unit, and the control unit may output thesolenoid excitation command for shifting the selector valve to thesecond position when the detection signal from the stickcontraction-side pressure sensor is inputted to the control unit.

For supplying the pilot pressurized oil in the avoidance pilot oil line50 to the stick control valve contraction-side pilot port 19 a, thehydraulic control circuit can also be structured in accordance with athird embodiment shown in FIG. 8. Note that the same leader-linenumerals denote the same components as in the first and secondembodiments and a detailed description thereof is omitted here.

In the third embodiment, a component corresponding to the selector valve33 in the above first embodiment is not provided in a stickcontraction-side oil line connecting a stick contraction-side pilotvalve 23A and a stick control valve contraction-side pilot port 19 a. Asolenoid proportional pressure reducing valve 56 on the stickcontraction side, which operates in accordance with a control commandfrom a control unit 32, and a third shuttle valve 57 are provided in thestick contraction-side oil line instead.

The third shuttle valve 57 has an inlet-side first port 57 a connectedto a third port (output port) 56 c of the solenoid proportional pressurereducing valve 56 on the stick contraction side, an inlet-side secondport 57 b connected to a third port (output port) 58 c of an avoidancesolenoid proportional pressure reducing valve 58 described later, and anoutlet-side port 57 c connected to the stick control valvecontraction-side pilot port 19 a. Of the pilot pressurized oilintroduced from each of the inlet-side first and second ports 57 a, 57b, the pilot pressurized oil on the higher pressure side is selected bythe third shuttle valve 57 and then delivered from the outlet-side port57 c thereof.

The avoidance solenoid proportional pressure reducing valve 58 operatesin accordance with a control command from the control unit 32, and has afirst port (input port) 58 a connected to the avoidance pilot oil line50.

When the stick-out manipulation is performed, the control unit 32outputs a control command to the solenoid proportional pressure reducingvalve 56 on the stick contraction side, thereby fully opening an outputvalve passage connecting a first port (input port) 56 a and the thirdport 56 c, and also outputs a control command to the avoidance solenoidproportional pressure reducing valve 58, thereby fully closing an outputvalve passage connecting the first port 58 a and the third port 58 c. Asa result, the third shuttle valve 57 selects the pilot pressurized oilfrom the solenoid proportional pressure reducing valve 56 on the stickcontraction side, and the selected pilot pressurized oil is supplied tothe stick control valve contraction-side pilot port 19 a. Thus, when thestick-out manipulation is performed, the stick-out operation is carriedout as per the manipulation.

On the other hand, when it is determined in a state of the stick-outmanipulation not being performed that the working implement 5 hasreached the outer boundary line of the interference prevention area H,the control unit 32 outputs a control command to the solenoidproportional pressure reducing valve 56 on the stick contraction side,thereby fully closing the output valve passage, and also outputs acontrol command to the avoidance solenoid proportional pressure reducingvalve 58, thereby fully opening the output valve passage. As a result,the third shuttle valve 57 selects the pilot pressurized oil from theavoidance solenoid proportional pressure reducing valve 58, and theselected pilot pressurized oil is supplied to the stick control valvecontraction-side pilot port 19 a. Thus when the working implement 5reaches the outer boundary line of the interference prevention area H inthe state where the stick-out manipulation is not performed, the pilotpressurized oil from the avoidance pilot oil line 50 is supplied to thestick control valve contraction-side pilot port 19 a via the avoidancesolenoid proportional pressure reducing valve 58, causing the stick-outoperation to be automatically carried out.

With the hydraulic control circuit described above, when a workingimplement enters an interference prevention area during operation, pilotpressurized oil is automatically supplied in the direction to move theworking implement away from the interference prevention area, enablingthe operation, or work, to be continued while avoiding the interferenceprevention area.

Also, the operation can be continued while avoiding the interferenceprevention area just by providing, in addition to a conventional circuitfor stopping the working implement, a pilot pump oil line and a selectorvalve in an oil line for supplying the pilot pressurized oil in thedirection to move a stick away from the interference prevention area.The invention contributes to simplifying the circuit and holding downany increase in cost.

What is claimed is:
 1. A hydraulic control circuit for a working machinecomprising a hydraulic actuator operated to move a working implement,and a pilot-operated directional control valve for controlling supply ofpressurized oil to said hydraulic actuator, said hydraulic controlcircuit including: a pressure control valve for controlling supply ofpilot pressurized oil to said directional control valve in accordancewith a command from a control unit; a pilot valve for delivering thepilot pressurized oil to said pressure control valve in accordance withmanipulation of a control member; a pilot pump oil line capable ofsupplying the pilot pressurized oil to said pressure control valve froma pilot oil pressure source without passing said pilot valve; and aselector valve for supplying the pilot pressurized oil delivered fromsaid pilot valve to said pressure control valve when said control memberis manipulated, and supplying the pilot pressurized oil from said pilotpump oil line to said pressure control valve when said control member isnot manipulated, said control unit including: determining means fordetermining whether said working implement has entered a presetinterference prevention area based on input signals from attitudedetecting means for detecting an attitude of said working implement; andinterference prevention control means for outputting a control commandto said pressure control valve, causing the pilot pressurized oil to besupplied to said pilot-operated directional control valve in thedirection to move said working implement away from the interferenceprevention area, when said determining means determines that saidworking implement has entered the preset interference prevention area.2. The hydraulic control circuit for a working machine according toclaim 1, wherein said hydraulic actuator for moving said workingimplement comprises a boom up-and-down moving cylinder for verticallyswinging an offset type boom which is swingable in the up-and-down andleft-and-right directions, a boom left-and-right moving cylinder forswinging said boom to the left and right, and a stick cylinder forswinging a stick back and forth which is supported to a fore end of saidboom to be swingable in the back-and-forth direction; said pressurecontrol valve, said pilot valve, said pilot pump oil line and saidselector valve are provided in an oil line for supplying the pilotpressurized oil to the directional control valve for said stick cylinderin the direction to move said stick away from the interferenceprevention area; and said pressure control valve and said pilot valveare provided in each of oil lines for supplying the pilot pressurizedoil to each of the directional control valves for said boom up-and-downmoving cylinder, said boom left-and-right moving cylinder, and saidstick cylinder in the direction to move said boom or said stick closertoward the interference prevention area.
 3. A hydraulic control circuitfor a working machine comprising first and second hydraulic actuatorsfor operating a working implement, and first and second pilot-operateddirectional control valves for respectively controlling supply ofpressurized oil to said hydraulic actuators, wherein said hydrauliccontrol circuit includes: interference prevention control means forpreventing said working implement from entering an interferenceprevention area set in advance to prevent interference between a body ofsaid working machine and said working implement, and said interferenceprevention control means includes a mechanism for operating said firsthydraulic actuator in the direction away from the interferenceprevention area, thereby continuing operation of said second hydraulicactuator while said working implement is prevented from entering theinterference prevention area when it is determined, at least in a stateof said second hydraulic actuator being operated, that said workingimplement has reached the interference prevention area, said mechanismincluding valve means for switching over the circuit such that pilotpressurized oil for operating said second hydraulic actuator is alsosupplied to a pilot oil line for operating said first hydraulic actuatorin the direction away from the interference prevention area.
 4. Thehydraulic control circuit for a working machine according to claim 3wherein said hydraulic control circuit includes first and secondapproaching-side pilot oil lines for supplying the pilot pressurized oilrespectively to said first and second directional control valves in thedirection of moving said working implement to approach the interferenceprevention area, first and second away-side pilot oil lines forsupplying the pilot pressurized oil respectively to said first andsecond directional control valves in the direction of moving saidworking implement away from the interference prevention area, and firstand second approaching- and away-side pilot valves for outputting thepilot pressurized oil respectively to said first and second approaching-and away-side pilot oil lines in accordance with manipulation of firstand second control members, and a pressure control valve for opening andclosing the pilot oil line in accordance with a command from saidinterference prevention control means provided at least in said firstapproaching-side pilot line.
 5. The hydraulic control circuit for aworking machine according to claim 4, wherein when said second hydraulicactuator is provided in plural number, said second directional controlvalve, said second approaching- and away-side pilot oil lines, saidsecond approaching- and away-side pilot valves are provided for each ofthe second hydraulic actuators, and the pilot pressurized oil deliveredfrom said second approaching-side pilot valve is supplied to said valvemeans after being joined with other pilot pressurized oil through ashuttle valve for selecting the pilot pressurized oil on the higherpressure side.
 6. The hydraulic control circuit for a working machineaccording to claim 4, wherein said valve means comprises a selectorvalve for switching over the circuit such that when the pilotpressurized oil is delivered from said first away-side pilot valve, thedelivered pilot pressurized oil is supplied to said first away-sidepilot oil line, and when the pilot pressurized oil is not delivered fromsaid first away-side pilot valve, the pilot pressurized oil deliveredfrom said second approaching-side pilot valve is supplied to said firstaway-side pilot oil line, and a pressure control valve for opening andclosing said first away-side pilot oil line in accordance with a commandfrom said interference prevention control means.
 7. The hydrauliccontrol circuit for a working machine according to claim 5, wherein saidvalve means comprises a selector valve for switching over the circuitsuch that when the pilot pressurized oil is delivered from said firstaway-side pilot valve, the delivered pilot pressurized oil is suppliedto said first away-side pilot oil line, and when the pilot pressurizedoil is not delivered from said first away-side pilot valve, the pilotpressurized oil delivered from said second approaching-side pilot valveis supplied to said first away-side pilot oil line, and a pressurecontrol valve for opening and closing said first away-side pilot oilline in accordance with a command from said interference preventioncontrol means.
 8. The hydraulic control circuit for a working machineaccording to claim 4, wherein said valve means comprises a pressurecontrol valve for outputting the pilot pressurized oil delivered fromsaid second approaching-side pilot valve in accordance with a commandfrom said interference prevention control means, and a shuttle valve forselecting one of the higher pressure side of the pilot pressurized oildelivered from said pressure control valve and the pilot pressurized oildelivered from said first away-side pilot valve and supplying theselected pilot pressurized oil to said first away-side pilot oil line.9. The hydraulic control circuit for a working machine according toclaim 5, wherein said valve means comprises a pressure control valve foroutputting the pilot pressurized oil delivered from said secondapproaching-side pilot valve in accordance with a command from saidinterference prevention control means, and a shuttle valve for selectingone of the higher pressure side of the pilot pressurized oil deliveredfrom said pressure control valve and the pilot pressurized oil deliveredfrom said first away-side pilot valve and supplying the selected pilotpressurized oil to said first away-side pilot oil line.
 10. Thehydraulic control circuit for a working machine according to claim 3,wherein said working machine is a hydraulic shovel including, as saidsecond hydraulic actuator, a boom up-and-down moving cylinder forvertically swinging an offset type boom which is swingable in theup-and-down and left-and-right directions, and an offset cylinder forswinging said boom to the left and right, and including, as said firsthydraulic actuator, a stick cylinder for swinging a stick back and forthwhich is supported to a fore end of said boom to be swingable in theback-and-forth direction.
 11. The hydraulic control circuit for aworking machine according to claim 4, wherein said working machine is ahydraulic shovel including, as said second hydraulic actuator, a boomup-and-down moving cylinder for vertically swinging an offset type boomwhich is swingable in the up-and-down and left-and-right directions, andan offset cylinder for swinging said boom to the left and right, andincluding, as said first hydraulic actuator, a stick cylinder forswinging a stick back and forth which is supported to a fore end of saidboom to be swingable in the back-and-forth direction.
 12. The hydrauliccontrol circuit for a working machine according to claim 5, wherein saidworking machine is a hydraulic shovel including, as said secondhydraulic actuator, a boom up-and-down moving cylinder for verticallyswinging an offset type boom which is swingable in the up-and-down andleft-and-right directions, and an offset cylinder for swinging said boomto the left and right, and including, as said first hydraulic actuator,a stick cylinder for swinging a stick back and forth which is supportedto a fore end of said boom to be swingable in the back-and-forthdirection.
 13. The hydraulic control circuit for a working machineaccording to claim 6, wherein said working machine is a hydraulic shovelincluding, as said second hydraulic actuator, a boom up-and-down movingcylinder for vertically swinging an offset type boom which is swingablein the up-and-down and left-and-right directions, and an offset cylinderfor swinging said boom to the left and right, and including, as saidfirst hydraulic actuator, a stick cylinder for swinging a stick back andforth which is supported to a fore end of said boom to be swingable inthe back-and-forth direction.
 14. The hydraulic control circuit for aworking machine according to claim 7, wherein said working machine is ahydraulic shovel including, as said second hydraulic actuator, a boomup-and-down moving cylinder for vertically swinging an offset type boomwhich is swingable in the up-and-down and left-and-right directions, andan offset cylinder for swinging said boom to the left and right, andincluding, as said first hydraulic actuator, a stick cylinder forswinging a stick back and forth which is supported to a fore end of saidboom to be swingable in the back-and-forth direction.